The present invention relates to a slab continuous casting machine, and more specifically to a slab continuous casting machine having an immersing nozzle replacing apparatus and a method of replacing an immersing nozzle.
The slab continuous casting machine described below is defined as the continuous casting machine for casting a slab of about 200 mm or less thick.
The conventional continuous casting machine has been typically used for casting the slab of 200 mm or more thick. However, there has been a recent tendency to directly cast the thin slab of 200 mm or less thick. This is because the thinner slab can omit a rolling process performed by a rolling mill in a subsequent step, although an end product cannot be directly cast by the continuous casting machine.
On the other hand, in the continuous casting machine, an immersing nozzle is essential to stably pour a molten steel from a tundish into a mold. A frequency of tundish maintenance greatly depends on a life of the immersing nozzle. A capability to replace the immersing nozzle during a casting is therefore important in order to reduce the frequency of tundish maintenance.
In the continuous casting machine for casting the slab of 200 mm or more thick, a replacement of the immersing nozzle during the casting is already carried out. For the replacement of the immersing nozzle, a nozzle holding cassette is disposed on an outer bottom portion of the tundish. A handling arm for gripping and carrying the immersing nozzle is also disposed near the mold. The replacement of the immersing nozzle in the continuous casting machine is performed in the following manner. During the casting, an operator operates the handling arm, whereby the new immersing nozzle is attached into the nozzle holding cassette and the old immersing nozzle is then removed from the nozzle holding cassette. The conventional handling arm is freely movable and does not include a guide mechanism for limiting a movement of the immersing nozzle in the mold. This is because a sufficient space between an inner wall of the mold and the immersing nozzle permits a little possibility that the immersing nozzle breaks a solidified shell of the molten steel formed in the mold.
However, in the slab continuous casting machine for casting the slab of 200 mm or less thick, since a distance between the immersing nozzle and the inner wall of the mold is shorter, the replacement of the immersing nozzle during the casting is not carried out. That is, in the slab continuous casting machine, when the replacement of the immersing nozzle is attempted by the use of the above-described handling arm, the following problem arises. Since the space between the inner wall of the mold and the immersing nozzle is very small, even if a little mistake in an operation of the handling arm occurs, the immersing nozzle is caused to come into contact with the solidified shell of the molten steel. This causes an accident in which the solidified shell is broken.